Experimental study on mechanical behavior of external prestressed FRP reinforced concrete beams
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摘要: 为了研究体外预应力复合材料筋混凝土梁的破坏特征和承载性能，对12根全FRP筋试验梁开展了三分点加载试验，其中体外预应力筋为碳纤维增强复合材料(CFRP)筋，受力筋和箍筋采用玻璃纤维增强复合材料(GFRP)筋。对比分析预应力水平、剪跨比、混凝土种类等因素变化对GFRP筋混凝土梁承载力的影响，推导了包含预应力筋应力增量影响的受弯承载力表达式，并将计算结果与试验结果进行对比。结果表明，无预应力梁的破坏主要由变形控制，施加预应力梁的破坏由变形控制转变为承载力控制。预应力FRP筋混凝土梁跨中挠度与预应力增量基本呈正比例关系。FRP筋梁承载力随剪跨比的增大而减小，且剪跨比对开裂荷载的影响更显著。混凝土种类对预应力梁开裂荷载的影响大，而对无预应力梁的开裂荷载和极限荷载影响较小。本文推导的预应力FRP筋混凝土梁承载力计算结果与实测值吻合较好。Abstract: This study proposes to investigate the failure characteristics and load-bearing performance of external prestressed composite reinforced concrete beams by conducting a three-point loading test on 12 full FRP reinforced concrete beams. These external prestressed concrete beams were reinforced with carbon fiber reinforced polymer(CFRP), while the stress reinforcement and stirrup were made of glass fiber reinforced polymer(GFRP). Specifically, the study compares the impact of prestress level, shear span ratio, and concrete type on the bearing capacity of GFRP reinforced concrete beams. derives an expression for flexural bearing capacity to account for the effect of stress increment of prestressed tendons, and is verified by experimental results. The test results indicate that the failure of non-prestressed FRP reinforced concrete beams is primarily governed by deformation, whereas applying prestress can shift the failure mode from deformation control to bearing capacity control. The mid-span deflection of the concrete beam is directly proportional to the increase in prestress. The bearing capacity of FRP beams decreases with an increase in shear span ratio, with particularly significant effect on cracking load. The effect of concrete type on the cracking load of prestressed beams surpasses its impact on the ultimate load, while it exerts minimal influence on cracking and ultimate load of non-prestressed beams. The calculated results for the bearing capacity of prestressed FRP reinforced concrete beams derived in this study align well with the measured values.
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Key words:
- external prestress /
- FRP bars /
- bearing capacity limit state /
- deformation /
- prestress level
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图 5 预应力筋拉断前后裂缝形态对比
Figure 5. Comparison of failure modes before and after prestressed tendon breaking
图 7 预应力FRP筋梁的截面应变分布
Figure 7. Strain distribution along the section of prestressed reinforcement beam with FRP tendons
图 8 试件挠度沿跨度分布曲线
Figure 8. Load-deflection distribution curves along the span of specimen
图 9 张拉预应力对比组混凝土梁荷载-挠度曲线
Figure 9. Load-deflection curves of FRP beams under different prestressing levels
图 10 预应力水平对混凝土梁开裂荷载及极限荷载的影响
Figure 10. Influence of prestress level on cracking load and ultimate load of concrete beams
图 11 不同剪跨比下FRP筋混凝土梁荷载-挠度曲线
Figure 11. Load-deflection curves of FRP beams with different shear span ratios
图 12 剪跨比对混凝土梁开裂荷载及极限荷载的影响
Figure 12. Influence of shear span ratio on cracking load and ultimate load of concrete beams
图 13 混凝土强度对混凝土梁开裂荷载及极限荷载的影响
Figure 13. Influence of concrete strength on cracking load and ultimate load of concrete beams
图 14 不同混凝土种类下FRP筋混凝土梁荷载-挠度曲线
Figure 14. Load-deflection curves of FRP beams under different concrete types
图 15 混凝土种类对梁开裂荷载及极限荷载的影响
Figure 15. Influence of concrete type on cracking load and ultimate load of concrete beam
图 16 预应力筋混凝土梁变形示意图
Figure 16. Deformation diagram of prestressed reinforced concrete beam
表 1 试验梁设计方案
Table 1. Design scheme of test specimens
梁号 混凝土种类 剪跨比 混凝土标号 预应力水平/% L1 SCC 3.75 C70 30 L2 SCC 3.75 C70 45 L3 SCC 3.75 C70 60 L4 SCC 2.68 C45 45 L5 SCC 3.75 C45 45 L6 SCC 4.44 C45 45 L7 普通 3.75 C45 45 L8 SCC 4.44 C45 0 L9 SCC 4.44 C70 0 L10 普通 4.44 C45 0 L11 SCC 3.75 C45 0 L12 普通 2.68 C45 0 注：SCC—自密实混凝土。 
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表 2 混凝土和FRP筋材料性能试验结果
Table 2. Test results of material properties of concrete and FRP bars
混凝土/筋材类型 设计标号 28 d强度/MPa 极限抗拉强度/MPa 弹性模量/GPa SCC C70 72.80 — — SCC C45 45.90 — — 普通 C45 46.00 — — CFRP-8 — — 2 724.00 190.22 GFRP-8 — — 1 348.00 54.70 GFRP-12 — — 1 105.00 48.54
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表 3 体外预应力筋混凝土梁理论计算结果
Table 3. Theoretical calculation results of external prestressed reinforced concrete beams
梁编号 计算挠度/mm 实际挠度/mm 比值 计算极限承载力/kN 实际承载力/kN 比值 L1 68.24 68.64 0.99 171.18 145.53 1.18 L2 47.41 60.87 0.78 141.37 128.18 1.10 L3 53.09 68.27 0.78 162.63 151.70 1.07 L4 35.91 33.00 1.09 148.69 114.00 1.30 L5 28.9 32.00 0.90 103.76 87.00 1.19 L6 64.62 64.74 1.00 140.54 118.88 1.18 L7 65.38 61.77 1.06 174.14 133.06 1.31 平均值 0.94 1.19 标准值 0.13 0.09 变异系数 0.13 0.08
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